----- Original Message ----- From: "Richard Brekne" <Richard.Brekne@grieg.uib.no> To: "Pianotech" <pianotech@ptg.org> Sent: October 21, 2003 11:04 AM Subject: Re: Soundboards: Thickness and Area > > Dont know what to say to this, except that its the first time I've heard > this explaintion. Everywhere else I look, and the times I've sat in on > demonstrations are as I have previously described. > > For example...taken from URL > http://www.phys.unsw.edu.au/~jw/chladni.html > > "How are Chladni patterns formed? > There are at least three different methods. > > The plate can be made to resonate by a powerful sound wave which is > tuned to the frequency of the desired mode. > > The plate can be bowed with a violin bow. This is easiest if one choses > a point that is a node for most of the modes that one doesn't want, but > not for the desired node. > > The plate can be excited mechanically or electromechanically at the > frequency of the desired mode." > Don't know what to say, Richard, except that sometimes you can't learn everything there is to know about a subject off the Internet. Hitting the thing with a hammer is not the best way to develop Chladni patterns, but it is one way. And, as I said, a rather crude one at that. Which is not to imply that might not be useful to the folks doing it. But, the soundboard is being excited mechanically at the frequency of the desired mode, in this case the fundamental. In fact it is being excited at most of its vibrating modes, at least those consistent with an impact from a relatively soft and probably fairly massive hammer. The soundboard, by its nature, will filter out energy at those frequencies it does not respond resonantly to and will break up -- however briefly -- to those that are resonant. The strongest of these will be found at the fundamental resonating mode of the soundboard assembly. Del
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